Kconfig: Fix incorrect CONFIG_STACK_SIZE values for X86 and ARM64

Commit 54229a7 (arm: Fix checkstack() to use correct stack size) didn't
quite hit the mark. Due to the crazy way our Kconfig includes work, It
accidentally set CONFIG_STACK_SIZE to 0 even on architectures that need
it.

This patch fixes the issue by moving everything back to a single entry
in src/Kconfig, making sure we end up with the intended numbers on all
architectures.

BRANCH=None
BUG=chrome-os-partner:34750
TEST=Built for Pinky, Urara, Falco and Ryu. Confirmed that the generated
.config contained CONFIG_STACK_SIZE=0x0 for the former two, and
CONFIG_STACK_SIZE=0x1000 for the latter.

Original-Change-Id: Ib18561925aafe7c74e6c4f0b10b55000a785e144
Original-Signed-off-by: Julius Werner <jwerner@chromium.org>
Original-Reviewed-on: https://chromium-review.googlesource.com/236753
Original-Reviewed-by: David Hendricks <dhendrix@chromium.org>

(cherry picked from commit c64b127e163f98162f3f7195b6ed09bd5a4b77c4)
Signed-off-by: Aaron Durbin <adurbin@chromium.org>

Change-Id: I2c747b04760bc97f43523596640bfb15317e5730
Reviewed-on: http://review.coreboot.org/9696
Reviewed-by: David Hendricks <dhendrix@chromium.org>
Reviewed-by: Edward O'Callaghan <edward.ocallaghan@koparo.com>
Tested-by: build bot (Jenkins)
diff --git a/src/Kconfig b/src/Kconfig
index 8a5d905..6cf3134 100644
--- a/src/Kconfig
+++ b/src/Kconfig
@@ -319,6 +319,7 @@
 
 config STACK_SIZE
 	hex
+	default 0x0 if (ARCH_RAMSTAGE_ARM || ARCH_RAMSTAGE_MIPS)
 	default 0x1000
 
 config MAX_CPUS